Tdma satellite communications system with an aperture window for acquisition

ABSTRACT

In a satellite transponder communication system operating in a time division multiple access mode, each earth station transmits data in a burst format. All bursts within a single transponder frame are synchronized to a special reference burst which contains no data communications. A single earth station sends out the reference burst as well as its normal burst, and in the case of multi transponders and multi transponder frames, the single reference station sends out all of the reference bursts for the various transponder frames. Data to be transmitted may be received in many different forms and included within the same burst because of the modular arrangement of the earth stations. Individual terrestrial interface modules receive data in various forms, convert the data into bit form which is compatible with the TDMA system, store the converted bit stream and hold the block of data until a multiplexer requests the block of data for inclusion into the earths station&#39;&#39;s transmitted burst. The arragnement of blocks of data within a burst and the timing and duration of a burst is controlled by digital words stored in a memory. Complete reordering of burst times and the arrangement of blocks of data within a burst is accomplished by changing the words stored in the memory. A system on the receive side of the earth station extracts blocks of data in selected bursts for conveyance to selected terrestrial interface modules. Acquisition of the proper burst time within each frame is accomplished by sending out a low power signal and monitoring its phase relative to the received frame reference. Apertures are provided to insure that no two earth stations are simultaneously in the acquisition mode.

llnited States atent 91 Schmidt et al.

[75] A Inventors: William G. Schmidt, Rockville; Ova G. Gabhard, Germantown, both of Md.; John M. Husted, Vienna, Va.;

Wilfrid G. Maillet, Oxon Hill; Marinus A. Bos, Rockville, both of Md.

[73] Assignee: Communications Satellite Corporation, Washington, DC.

[22] Filed: Aug. 11, 1971 [21] Appl. No.: 170,932

[52] U.S. Cl. ..l79/15 BS, 325/4, 178/695 R [51] ..H04j 3/06 [58] Field of Search ..178/69.5 R;

[5 6] References Cited UNlTED STATES PATENTS 3,593,138 7/1971 Dunn ..325/4 Primary Examiner-Ralph D. Blakeslee Atrorney-Richard C. Sughrue et a1.

ABSTRACT- In a satellite transponder communication system MASTER FRAME operating in a time division multiple access mode, each earth station transmits data in a burst format. All bursts within a single transponder frame are synchronized to a special reference burst which contains no data communications. A single earth station sends out the reference burst as well as its normal burst, and in the case of multi transponders and multi transponder frames, the single reference station sends out all of the reference bursts for the various transponder frames. Data to be transmitted may be received in many different forms and included within the same burst because of the modular arrangement of the earth stations. Individual terrestrial interface modules receive data in various forms, convert the data into bit form which is compatible with the TDMA system, store the converted bit stream and hold the block of data until a multiplexer requests the block of data for inclusion into the earths stations transmitted burst. The arragnement of blocks of data within a burst and the timing and duration of a burst is controlled by digital words stored in a memory. Complete reordering of burst times and the arrangement of blocks of data within a burst is accomplished by changing the words stored in the memory. A system on the receive side of the earth station extracts blocks of data in selected bursts for conveyance to selected terrestrial interface modules. Acquisition of the proper burst time within each frame is accomplished by sending out a low power signal and monitoring its phase relative to the received frame reference. Apertures are provided to insure that no two earth stations are simultaneously in the acquisition mode.

4 Claims, 27 Drawing Figures RECEIVE DETECTOR (REF PULSE) RESET OSCILLATOR START PULSE 2:33a ACQUISITION wmnoa U304 COUNTER GENERATOR FUNCTION 1r TRANSlllT LOCK/UNLOCK I GENERATOR MODULATOR musun B06 SYNCHRONIZER OSCILLATOR RECEIVE RECEIVE l B08 c ouas mou ACOUISIIION 7v 1F RECEIVE PULSE PULSE -l DEMODULATOR DETECTION Patented May 1, 1973 3,730,998

21 Sheets-Sheet l TERRESTRIAL INTERFACE MODULES Q TERR STRIAL INTERFACE 04 moms I06 0 ||6'\ 1i) l [08 :9 5 g E :D TDMA TDMA 1) g f 5 0 TRANSMIT RECEIVE' 6 3 g g g MULTIPLEX DEMULTIPLEX g 5 J P- J g 1 CONTROL CONTROL 2 I c: H m 1 H6 :2

TRANSMIT SIDE RECEIVE SIDE N 250 sac. 210

4 STA. A sum smc sm smz ,J L\\-\\ /F"//J ans [8/16 4a 20 8? F I I 1 1 I I GUARD CARRIERGSYMBOL umous STAS ANDARD TIME mums RECOVERY woan 10.0 PREAMBLE W 133 SYNCH I gg 1 202 i 204 BU WE: 40 A 20 s 4 |e BITS '1 I '1 '1" 'r "I I GUARD CARRIERGSYMBOL- umouE STA? TIME TIMING RECOVERY WORD m. G WIRE I 206 J l 208 j I mm mm mm mm INVENTORS WILLIAM G. SCHMIDT, OVA 0. GABBARD, [In 2 JOHN M. HUSTED,WILFRID GMAILLET,

MARINUS A. B08

BY I

Zfn a If Mere-3f ATTORNEYS Patented May 1, 1973 21 Sheets-Sheet 2 nowN' CONVERTERS -31s SWITCH $320 3T2 l L r322 TRANSMIT RECEIVE MULTIPLEXEIR a CONTROL & CONTROL DEMULTIPLEXER 30o s24 I TIN. TTN HM. TNN. TIN. TIN.

TERREsTRNN INTERFACE TERRESTRIAL INTERFACE EQUIPMENT EQUIPMENT u TDMA FRAME j T 7 A| B| C| 0 E| F| 6 TRQI 2 2 2 2 *2 2 TM SYNCH REFERENCE BURSTS m3 D4 E4 A4 B4 C4 [Rg4 s s 5 5 5 5 5 5 5 "5 "5&5 5 5 SYNCH REFERENCE. BURST Patented May 1, 1973 21 Sheets-Sheet 9 :20 1II||IIIII|IO O 9-H w @22 mm E5 5 E 5E m Ni: 0 55m :75 E238 E580 xocwwowza a 55m 02s: 5m us: E 620 52 1 NE so; u 05; AF 2 E22 -25 M Q2 9 525 555 Q81 9 2% BE 3 is 2: 323m :2: 89 m 5% is: v i s20 22 22 3% E5. :52 202 3% :2: 5E on 5% m m 52% o 5% =2: 29:; :2: A l u 558 a 22 as: 5555 m w m h a3 5% 2925 m W E Na; 82 m w Patented May 1, 1973 21 Sheets-Sheet 12 V630 32.5 3:2: 5&2: kmtqm Ca. V

. 83% m3 $252 AH Tia:

=2 3 A was 52; 32 M12.

was E5333 QM GE Patented May 1, 1973 21 Sheets-Sheet 1 4 OSCILLATOR y no] m 2Q PSK MOD START 4kHz EMQ ZSOALSEC.

500,1(SEC.

Patented May I, 1973 21 Sheets-Sheet 18 (I600 BURST MODE DATA W COMPRESSION CLOCK BUFFER 3 DEcoDEx T DA COUNTER, DECODER cDDE aPHAsE DETEcTDR DECODE GENERATOR START OF FRAME I606 DECODE x-| END OF FRAME [I702 CONTINUOUS DATA EXPANSION INFORMATION 5 CONTINUOUS CLOCK j BUFFER SIGNALLING I706 DEMULTIPLEXER I @]i x X+l X-l "0O x DuRsT DATA HOB/ X X+I or X' X+| DEcoDER l704 PHASE FRAME REFERENCE DETEcToR 

1. In a TDMA satellite communications system of the type wherein multiple earth stations transmit respective bursts of informatioN at certain times within a TDMA frame period, and wherein acquisition of the proper frame position for the burst or bursts of any station is accomplished by transmitting and receiving a special acquisition signal and adjusting the phase of said signal in accordance with the relative positions of the received acquisition signals and the time slot of said frame assigned to said any station to position said received acquisition signals within said assigned time slot, the improvement comprising, means for dividing the time among all said stations during which acquisition transmission is enabled to prevent any substantial time overlap of acquisition signal transmission from any two or more stations.
 2. A TDMA system as claimed in claim 1 wherein said means for dividing comprises, a. means for periodically transmitting a special signal within a burst from one of said earth stations, b. means at each of said earth stations responsive to the receipt and detection of said special signal for generating a fixed duration gate signal a pre-established time following said receipt and detection, said pre-established time being different for each said station, and c. means responsive to said gate signal for preventing transmission of said acquisition signals except during the duration of said aperture gate.
 3. A TDMA system as claimed in claim 2 wherein said means for periodically transmitting comprises, means at a designated reference station for periodically substituting the complement of a reference unique word for a reference unique word which is normally sent in a burst from said designated reference station.
 4. A TDMA satellite communication system as claimed in claim 3 wherein the period between transmission of said special signal is at least as long as 1 minute. 